1. Field of the Invention
The present invention generally relates to all-optical demultiplexers and interferometers used for demultiplexing data.
2. Background Information
Conventional wavelength division multiplexing (WDM) systems efficiently use bandwidth in existing fiber-optic telecommunication infrastructures. Such systems provide point-to-point optical transmission at high aggregate rates ( greater than 100 Gb/s) without compromising on high performance. Future requirements of digital communication networks indicate that increased data-rate capacity is critical to a service provider""s success in the market. Ultimately, all-optical networks will replace today""s optical/electrical networks that suffer from the bottlenecking effects of optical-to-electrical-to-optical conversions due to the limited capacity of electronic devices. Devices that can optically process data without converting it to an electronic format are essential to this network capacity evolution.
Several forecasts have predicted that there will be a tremendous growth in the sensor market. In contrast to the classical sensors based largely upon the measurement of electrical parameters such as variable resistance or capacitance, modern sensors make use of a variety of novel phenomena. More importantly, these sensors are directly suitable for digital control and also have a degree of smartness incorporated in them to combat problems of nonlinearity and long term drift. Several key technologies are likely to play a major role in the sensors of the future. Microelectromechanical (MEM) sensors have tremendous potential as smart sensors. Fiber optics based sensors are also emerging as a viable and competitive technology. While many types of stand alone sensors are available, only some of them can be considered for integration with smart structures. Among these, fiber optic sensors are in the forefront in their choice for incorporation into materials and structures made of carbon and glass fiber reinforced polymer composites.
The advantages of fiber optic sensors (FOS) include freedom from EMI, wide bandwidth, compactness, geometric versatility and economy. In general, FOS is characterized by high sensitivity when compared to other types of sensors. FOS is also passive in nature due to the dielectric construction. Many signal processing devices (e.g., splitters, combiners, multiplexers, filters, delay lines) can also be made of fiber elements, thus enabling the realization of an all-fiber measuring system. Recently, photonic circuits (Integrated Optics) has been proposed as a single chip optical device or signal processing element which enables miniaturization, batch production, economy and enhanced capabilities.
A fiber optic sensor in general consists of a source of light, a length of sensing (and transmission) fiber, a photodetector, demodulation, processing and display optics and the required electronics. Interferometric (phase) sensors are based on the detection of changes in the phase of light emerging out of a single mode fiber. Interferometric fiber optic sensors are by far the most commonly used sensors since they offer the best performance.
A deficiency with prior art interferometers is that they cannot be xe2x80x9ctime tunedxe2x80x9d to handle different demultiplexing requirements. Presently, a different interferometer must be used for different data stream reading applications.
The present invention provides for the use of one or more variable time delay elements that enable the selection of desired digital bits or groups of bits in an all-optical data packet or all-optical data burst, while suppressing all other undesirable bits. The adjustment of the time delay value(s) associated with the variable time delay elements may be carried out to handle multiple demultiplexing requirements. Each requirement may use a different data stream reading application.
The present invention also provides for the monolithic integration of a variety of optical device structures construing the present invention, which together may be used to produce superior performance and increased utility over the prior art.